The blanking process plays an essential role in production and processing and is applied widely in manufacturing industries such as electronic product panels, mobile phone casings, terminals, metal gears, sheet metal cutting, metal tools (e.g., wrench and screwdriver), vehicle housings, sheet metal, wheel rims, etc. As shown in FIG. 10 (prior art), the structure of conventional blanking device/system is simple and comprises a punch 40, a blank holder 42, a die 43 and a sheet stock 8. The burnish length of blanked product from a conventional blanking device/system is about 30%-50% of the total blank thickness, which is not acceptable for products required 100% burnish length. To address this problem, a fine blanking device was invented by Fritz Schiess (Germany patent number 371004 filed in 1922) and has been used until today. As shown in FIG. 11 (prior art), compared to the dies for conventional blanking, the dies for fine blanking have a V-shaped ring 52b disposed on the blank holder 52 (the “upper die”). The conventional fine blanking device of FIG. 11 also comprises a punch 50, a die 53 (the “bottom die” or “mother die”), and an ejector chamber 54. The V-shaped ring is to reduce the fracture zone by increasing the hydrostatic pressure at the area on both sides of the sheet stock around the cutting edge of the punch or the mother die. Although conventional fine blanking process can reduce fracture zone (by around 80%-90% burnish length), the remaining 10-20% fracture zone with sunk angles and roll-overs seriously affects the quality of blanked products. Furthermore, the V-shaped ring used in the conventional fine blanking pierces into the product during the fine blanking process and many problems are thus arisen. For example: (1) rings with complex configuration other than a circular one are difficult to manufacture; therefore conventional fine blanking is not applicable to the blanking of products with complex configuration; (2) the difficulty in maintenance: fractures of V-shaped ring which occur due to stress concentration after thousands of blanking require repairs and result in higher maintenance cost; (3) for blanking of sheet stock with larger area, even circular V-shaped ring is difficult to manufacture and maintain; and a V-shaped ring cannot be pressed into the sheet material too deep due to its wedge-shape in nature, and thus conventional fine blanking is not applicable to thicker sheet stock (e.g., more than 10 mm in thickness), greatly restricting the application of conventional fine blanking.
Taking high precision three-lobe pumps and cycloid-shaped gears, and commonly used thicker spur gear as examples, these products cannot be manufactured using conventional fine blanking. FIG. 12 (prior art) shows a prior art (Int. J. Adv. Manuf. Technol. (2013 68:2761-2769)) aiming at improving conventional fine blanking by forming a V-shaped cavity 8a on a sheet stock 8, and then applying a hydraulic pressure through a hydraulic runner 62a of a blank holder 62. The fine blanking system of FIG. 12 also comprises a punch 60, a back pressure chamber 66, a hydraulic runner 66a and a mother die module 64. A means for sealing 15 is disposed between the sheet stock 8 and the blank holder 62. A means for sealing 15 is also disposed between the sheet stock 8 and the mother die module 64. Using the hydraulic pressure applied to the V-shaped cavity 8a to replace the V-shaped ring makes the control of the pressure possible. Although this prior art improves the conventional fine blanking in several aspects, such as reducing die production and maintenance costs and being applicable to thicker and complex products, the V-shaped cavity 8a makes the sheet stock 8 difficult to be constrained by the blank holder 62. Therefore, the problems of sunk angles and roll-overs still remain.
In view of the foregoing, it is urgently desired in this industry to develop a fine blanking device which is applicable for mass production without cost increase, and is applicable to thicker or larger and various complex configuration sheet stocks and in the same time reduces the sunk angles and roll-overs.